Gas dissolved water producing apparatus and method thereof and ultrasonic cleaning equipment and method thereof

ABSTRACT

A gas dissolved water producing apparatus includes a gas dissolving section, a gas channel for guiding a gas into the dissolving section, a first water channel for guiding water into the dissolving section, a gas dissolved water discharge channel, and a second water channel for guiding the water without passing through the dissolving section. The second water channel joins the gas dissolved water discharge channel to control the solution gas dissolved in the gas dissolved water can be controlled to a prescribed level of concentration.

TECHNICAL FIELD

The present invention relates to an aqueous solution producingapparatus, in which the aqueous solution contains a gas dissolvedtherein, (hereafter referred to as gas dissolved water producingapparatus) and a method thereof. In particular, the invention relates toa gas dissolved water producing apparatus and a method of producing agas dissolved water used in precision machineries, electronic industriesand medical and food industries.

BACKGROUND OF ART

As shown in FIG. 10, in a prior art gas dissolved water producingapparatus 201, a gas to be dissolved (hereafter referred to as solutiongas) 103 is typically introduced into an outer side of a hollow fibermembrane 102 incorporated in a processing tank 111, and the gas is thendissolved through the hollow fiber membrane 102 into water to be treated104 introduced into an inner side of the hollow fiber membrane 102, soas to produce a gas dissolved water 105.

The water to be treated 104 is fed by a pump 117 at a prescribed flowrate “q” to the inner side of the hollow fiber membrane 102 via a filter118 and a flow meter 119. A flow rate signal 120 (illustrated by abroken line in the drawing) from the flow meter 119 is sent to acontroller 121, which in turn sends a flow rate control signal 122(illustrated by another broken line in the drawing) to a motor (notshown) for driving the pump 117, which is equipped with a revolutionspeed control unit (not shown). Therefore, the revolution speed of themotor can be controlled such that the pump 117 provides a prescribedflow rate “q”.

The solution gas 103 passes through a flow meter 116, where a flow rateis controlled to a prescribed level, and is sent to an outer side of thehollow fiber membrane 102 approximately under an ambient pressure. Thegas is dissolved in water to be treated 104 through the hollow fibermembrane 102, while a residual gas is decomposed in an exhaust gasdecomposing tower 130 with the aid of a catalyst (not shown) and isemitted as an exhaust gas 106.

In the conventional gas dissolved water producing apparatus discussedabove, a concentration of a solution gas dissolved in a produced aqueoussolution (gas dissolved water) is a saturated concentration of asolution gas under a pressure for supplying the solution gas (typicallyan ambient pressure, which is a cleaning pressure under which cleaningis performed by using the gas dissolved water). However, in precisionmachineries, electronic industries, and medical and food industries,gentle cleaning of workpieces may be required so as to avoid any damage.Thus, it is desired to produce a gas dissolved water having aconcentration of solution gas in a gas dissolved water not greater thana saturated concentration at a cleaning pressure. The need for such acleaning process is especially necessary for device wafers such assemiconductor wafers, which have micro-fabricated wiring. There istherefore an increasing demand for cleaning by use of functional water,such as water containing nitrogen, water containing ozone, or watercontaining oxygen, with the concentration controlled to a desired levelbelow a saturated concentration.

Such a gas dissolved water can be produced by, for example, thefollowing procedures. After the solution gas has been supplied to theouter side of the hollow fiber membrane, supply of the solution gas issuspended, with only the water to be treated being continuously suppliedto dissolve the solution gas into the water to be treated. Consequently,pressure in the outer side of the hollow fiber membrane decreases, andthe solution gas dissolves into the water to be treated and reaches asaturated concentration under the decreased pressure level. Once theconcentration has reached a desired value, the solution gas is againsupplied into the outer side of the hollow fiber membrane, such that thepressure level can be maintained. As a result, the concentration of thesolution gas dissolved in the gas dissolved water is made lower than asaturated concentration in the case of supplying the solution gas underambient pressure. However, disadvantageously, it takes a long time forpressure in the outer side of the hollow fiber membrane to reach theabove-described pressure which is lower than ambient pressure. Besides,there is also a fear that a gas other than the targeted solution gas maybecome mixed with the solution gas under a pressure lower than ambientpressure.

The present invention has been made in light of the situation describedabove, and has as its object the provision of a gas dissolved waterproducing apparatus and a method therefor which is capable of producinga gas dissolved water having a concentration of a dissolved solution gasnot greater than a saturated concentration under ambient pressure, bothrapidly and efficiently.

SUMMARY OF THE INVENTION

To accomplish the object described above, according to the presentinvention, there is provided a gas dissolved water producing apparatus1, in which a solution gas 3 is dissolved in water to be treated 4 so asto produce gas dissolved water 5. The apparatus includes, as shown inFIG. 1: a dissolving section 11 for dissolving the solution gas 3 intothe water to be treated 4; a solution gas supply channel 12 for guidingthe solution gas 3 into the dissolving section 11; a first supplychannel for the water to be treated 13 for guiding the water to betreated 4 into the dissolving section 11; a gas dissolved waterdischarge channel 14 for guiding the gas dissolved water 5 from thedissolving section 11; and a second supply channel for the water to betreated 15 for guiding the water to be treated 4 without the waterpassing through the dissolving section 11. The second supply channel forthe water to be treated 15 joins the gas dissolved water dischargechannel 14, and the water to be treated 4 which has been guided throughthe second supply channel for the water to be treated 15 dilutes the gasdissolved water 5 so that the solution gas dissolved in the gasdissolved water 5 can be controlled to a prescribed level ofconcentration.

In the configuration described above, the apparatus includes thesolution gas supply channel 12, the first supply channel for the waterto be treated 13, the second supply channel for the water to be treated15, and the gas dissolved water discharge channel 14, in which thesecond supply channel for the water to be treated 15 joins the gasdissolved water discharge channel 14. Thus, the solution gas dissolvedin the gas dissolved water 5 can be diluted to a prescribed level ofconcentration with the water to be treated 4 which has been guidedthrough the second supply channel for the water to be treated 15. As aresult, the apparatus is able to produce a gas dissolved water 31 havinga concentration of dissolved solution gas not greater than a saturatedconcentration, both rapidly and efficiently.

According to the present invention, there is also provided a gasdissolved water producing apparatus 1 as described above, in which, asshown in FIG. 1, the second supply channel for the water to be treated15 is branched-off from the first supply channel for the water to betreated 13 so as to form a bypass channel 15 for bypassing thedissolving section 11.

With this configuration, since the second supply channel for the waterto be treated 15 branches-off from the first supply channel for thewater to be treated 13 to form the bypass channel 15 for bypassing thedissolving section 11, it is possible to simplify the channelconfiguration.

According to the present invention, there is also provided a gasdissolved water producing apparatus as described above, in which, asshown in FIG. 1 and FIG. 2, the dissolving section 11 comprises a hollowfiber membrane 2 wherein the solution gas 3 is introduced into one sideof the hollow fiber membrane 2, and the water to be treated 4 isintroduced into the other side of the hollow fiber membrane 2 so as togenerate the gas dissolved water 5.

The dissolving section 11 comprises the hollow fiber membrane 2, and thesolution gas 3 is introduced into one side of the hollow fiber membrane2 and the water to be treated 4 is introduced into the other side of thehollow fiber membrane 2, thereby generating the gas dissolved water 5.As a result, the apparatus is able to generate a gas dissolved waterrapidly and efficiently that includes no residual minute air bubbles orimpurities. It is to be noted that one side (the first side) of thehollow fiber membrane designates either the inner or the outer sidethereof, and the other side (the second side) of the hollow fibermembrane designates a side opposite to the first side, either the outeror the inner side thereof.

According to the present invention, there is also provided a gasdissolved water producing apparatus 1 as described above, the apparatusfurther comprising, as shown in FIG. 1: either a first flow rateregulating means 23 or a second flow rate regulating means 24. The firstflow rate regulating means 23 is disposed in the first supply channelfor the water to be treated 13 at a downstream side of a branch section13A or in the gas dissolved water discharge channel 14 at an upstreamside of a joining section 14A where the second supply channel for thewater to be treated 15 joins the gas dissolved water discharge channel14, and functions to regulate a flow rate Q1 of the water to be treated4 flowing through the dissolving section 11. The second flow rateregulating means 24 is disposed in the bypass channel 15 and functionsto regulate a flow rate Q2 of the water to be treated 4 bypassing thedissolving section 11. A dissolved solution gas concentration measuringmeans 26 is disposed in the gas dissolved water discharge channel 14 ata downstream side of the joining section 14A for measuring the dissolvedsolution gas concentration in the gas dissolved water 31; and a secondcontrol means 28 is provided for controlling either the first flow rateregulating means 23 or the second flow rate regulating means 24, basedon the dissolved solution gas concentration measured by the dissolvedsolution gas concentration measuring means 26. Therefore, the dissolvedsolution gas concentration can be controlled to the prescribed level.

By the configuration described above, since the apparatus compriseseither the first flow rate regulating means 23 or the second flow rateregulating means 24, the dissolved solution gas concentration measuringmeans 26, and the second control means 28, the second control means 28controls either the first flow rate regulating means 23 or the secondflow rate regulating means 24 based on a dissolved solution gasconcentration measured by the dissolved solution gas concentrationmeasuring means 26 so that a dissolved solution gas concentration can becontrolled to a prescribed level. Thus, the apparatus can produce thegas dissolved water 31 having a dissolved solution gas concentration notgreater than a saturated concentration both rapidly and efficiently. Itis to be understood that the gas dissolved water producing apparatus 1may comprise both of the means 23, 24 (the first flow rate regulatingmeans 23 and the second flow rate regulating means 24) and in such acase both of means 23 and 24 can be controlled in such a way that thedissolved solution gas concentration, as measured, can be controlled toa prescribed level.

To accomplish the object described above, according to the presentinvention, there is provided a gas dissolved water producing methodcomprising, as illustrated in FIG. 1: a first step of introducing thesolution gas 3 into the dissolving section 11 where the solution gas 3is to be dissolved into the water to be treated 4; a second step ofintroducing the water to be treated 4 into the dissolving section 11; athird step of dissolving the solution gas 3 into the water to be treated4 in the dissolving section 11 to produce the gas dissolved water 5; anda fourth step of mixing the water to be treated 4 not passing throughthe dissolving section 11 into the gas dissolved water 5 so that thesolution gas 3 dissolved in the gas dissolved water 31 after the mixingprocess can be controlled to the prescribed level of concentration.

According to the present invention, there is provided a gas dissolvedwater producing method according to the present invention, in which, asshown in FIG. 1, control in the fourth step is performed by controllinga ratio of the flow rate Q1 of the water to be treated 4 passing throughthe dissolving section 11 to the flow rate Q2 of the water to be treated4 not passing through the dissolving section 11.

To accomplish the object described above, according to the presentinvention, there is provided ultrasonic cleaning equipment 101comprising, as shown in FIG. 6 and FIG. 7: a gas dissolved waterproducing apparatus 1 as described above; and an ultrasonic wavetransmitting device 157 for imparting ultrasonic energy to the gasdissolved water 31 when a workpiece to be cleaned W1 is cleaned with thegas dissolved water 31 produced by the gas dissolved water producingapparatus 1.

With such a configuration, since the apparatus includes the gasdissolved water producing apparatus 1, and the ultrasonic wavetransmitting device 157, and ultrasonic energy is imparted to the gasdissolved water 31, which has been produced by the gas dissolved waterproducing apparatus 1, when the workpiece to be cleaned W1 is to becleaned with the gas dissolved water 31, the gas dissolved water 31 towhich ultrasonic energy has been imparted can be used as a cleaningliquid, and the gas dissolved water 31 having a concentration controlledto the saturated concentration is suitable for use as a cleaning liquid,whereby the workpiece to be cleaned W1 can be more effectively cleaned.To accomplish the object described above, there is provided anultrasonic cleaning method comprising: a producing step of producing thegas dissolved water according to the gas dissolved water producingmethod described above; an energy imparting process for imparting theultrasonic energy to the gas dissolved water which has been produced bythe producing process; and a cleaning process for cleaning the workpieceto be cleaned, by using the gas dissolved water to which the ultrasonicenergy has been imparted in the energy imparting process, as thecleaning water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a configuration of a gas dissolvedwater producing apparatus of an embodiment according to the presentinvention;

FIG. 2 is a schematic sectional view illustrating a configuration of aprocessing tank;

FIG. 3 is a diagram illustrating an experimental data of a nitrogen gasconcentration as a function of time, in the case where nitrogen gas isused as a solution gas for producing a gas dissolved water with anitrogen gas concentration of 6 ppm, in the gas dissolved waterproducing apparatus of the present invention;

FIG. 4 is a diagram illustrating other experimental data of a nitrogengas concentration as a function of time, in the case where the nitrogengas is used as the solution gas for producing the gas dissolved waterwith the nitrogen gas concentration of 10 ppm, in the gas dissolvedwater producing apparatus of the present invention;

FIG. 5 is a diagram illustrating still another experimental data of anitrogen gas concentration as a function of time, in the case where thenitrogen gas is used as the solution gas for producing the gas dissolvedwater with the nitrogen gas concentration of 13 ppm, in the gasdissolved water producing apparatus of the present invention;

FIG. 6 is a perspective view of ultrasonic cleaning equipment forcleaning a wafer by using a gas dissolved water produced by the gasdissolved water producing apparatus of FIG. 1;

FIG. 7 is a sectional view of a mega sonic cleaning nozzle employed inthe wafer cleaning equipment of FIG. 6;

FIG. 8 is a block diagram illustrating a configuration of an ultrasoniccleaning equipment for a wafer according to another embodiment of thepresent invention;

FIG. 9 is a perspective view of a cleaning liquid supply nozzle employedin the ultrasonic cleaning equipment of FIG. 8; and

FIG. 10 is a flow diagram illustrating a configuration of a gasdissolved water producing apparatus according to a prior art.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will now be describedbelow with reference to the attached drawings. It is to be appreciatedthat in respective drawings, those parts which are the same or similarto one another are designated by the same or similar reference numerals,and any duplicated descriptions will be omitted.

A configuration of a gas dissolved water producing apparatus 1 accordingto the present invention will be described with reference to FIG. 1. Thegas dissolved water producing apparatus 1 comprises a processing tank 11serving as a dissolving section with a hollow fiber membrane 2 (see FIG.2) incorporated therein. A solution gas supply piping 12 serves as asolution gas supply channel for delivering a solution gas 3 from asolution gas source 7, and a supply piping for a water to be treated 13serves as a first supply channel for the water to be treated fordelivering the water to be treated 4 from a source of the water to betreated 8. A gas dissolved water discharge piping 14 serves as a gasdissolved water discharge channel for guiding a gas dissolved water 5, abypass piping for the water to be treated 15 serves as a bypass channel,which branches off from the supply piping for the water to be treated 13and bypasses the processing tank 11 or the hollow fiber membrane 2 tojoin the gas dissolved water discharge piping 14, and a gas dissolvedwater drain piping 25 branches off from the gas dissolved waterdischarge piping 14.

As shown in FIG. 2, the processing tank 11 has a first inlet nozzle 41disposed in a lower side peripheral portion thereof, a first outletnozzle 42 disposed in an upper side peripheral portion thereof, a secondinlet nozzle 43 disposed in a top portion thereof, and a second outletnozzle 44 disposed in a bottom portion thereof. A plurality of hollowfiber membranes 2 formed into a hollow cylinder with a thinner wallthickness are arranged in a vertical direction in the processing tank 11so as to be incorporated therein.

The solution gas supply piping 12 is connected to the first inlet nozzle41 of the processing tank 11 to communicate with the outer side of thehollow fiber membrane 2. The supply piping for the water to be treated13 is connected to the second inlet nozzle 43 of the processing tank 11to communicate with the inner side of the hollow fiber membrane 2. Thegas dissolved water discharge piping 14 is connected to the secondoutlet nozzle 44 of the processing tank 11 to communicate with the outerside of the hollow fiber membrane 2. To the first outlet nozzle 42 ofthe processing tank 11 is connected an exhaust gas piping 45, which willbe explained later.

Referring again to FIG. 1, the explanation will be continued. The bypasspiping for the water to be treated 15 branches off at a branch section13A from the supply piping for the water to be treated 13, and joins thegas dissolved water discharge piping 14 at a joining section 14A.Accordingly, assuming that a flow rate of the water to be treated 4supplied to the supply piping for the water to be treated 13 isdesignated as “Q”, a flow rate of the water to be treated 4 suppliedfrom the supply piping for the water to be treated 13 to the inner sideof the hollow fiber membrane 2 is designated as “Q1”, and a flow rate ofthe water to be treated 4 branching off from the supply piping for thewater to be treated 13 and flowing through the bypass piping for thewater to be treated 15 is designated as “Q2”, then a relationshipQ=Q1+Q2 is established (including a case of Q1 or Q2 being equal to 0).In this embodiment, the flow rate of the gas dissolved water 5 flowingfrom the inner side of the hollow fiber membrane 2 into the gasdissolved water discharge piping 14 is Q1, and the flow rate of the gasdissolved water 31 which is discharged from the gas dissolved waterdischarge piping 14 after the water to be treated 4 having the flow rateQ2 joins and dilutes the gas dissolved water, is Q.

It is to be noted that the gas dissolved water exiting from theprocessing tank 11 and flowing through the gas dissolved water dischargepiping 14 that has not yet reached the joining section 14A is indicatedby the reference numeral 5, while the gas dissolved water that hasjoined the water to be treated 4 which has not passed through theprocessing tank 11, at the joining section 14A and has been dilutedthereby is indicated by the reference numeral 31. It is also to beunderstood that even if a flow rate of the water to be treated 4 notpassing through the processing tank 11 is zero and thus there is nodilution to be conducted, the gas dissolved water flowing through thegas dissolved water discharge piping 14 in the downstream side of thejoining section 14A is still represented by the reference numeral 31.

A solution gas flow regulator 16 is installed in the solution gas supplypiping 12 so as to regulate the flow rate of the solution gas 3 suppliedto the outer side of the hollow fiber membrane 2, to the prescribedvalue. A pump 17 driven by a motor (not shown) is installed in thesupply piping for the water to be treated 13 so as to pump the suppliedwater to be treated 4 into the processing tank 11. A filter 18 isinstalled in the supply piping for the water to be treated 13 at adownstream side of the pump 17 to eliminate foreign substances includedin the water to be treated 4. A flow meter 19 is installed in the supplypiping for the water to be treated 13 at a downstream side of the pump17 for functioning as a flow rate measuring means, and the flow meter 19sends a flow rate signal 20 (indicated by the broken line in thedrawing) to a first controller 21 functioning as the first controlmeans, which in turn sends a flow rate control signal 22 (indicated alsoby the broken line in the drawing) to the pump motor (not shown)equipped with a revolution speed control unit (not shown)(the signal isshown to be sent to the pump 17 in the drawing. Thus, the revolutionspeed of the motor can be controlled so that the discharge flow rate ofthe pump 17 (i.e., the supply flow rate Q of the water to be treated 4to the gas dissolved water producing apparatus 1) can be regulated tothe prescribed flow rate. It is to be noted that the pump 17, the filter18, and the flow meter 19 are all located in the upstream side of thebranch section 13A.

A first flow regulator for the water to be treated 23 functioning as thefirst flow rate regulating means is installed in the supply piping forthe water to be treated 13 at a downstream side of the branch section13A, and the second flow regulator for the water to be treated 24functioning as the second flow rate regulating means is installed in thebypass piping for the water to be treated 15. Although the first flowregulator for the water to be treated 23 may be installed in the supplypiping for the water to be treated 13 either at an upstream or adownstream side of the hollow fiber membrane 2, the installation in thedownstream side of the hollow fiber membrane 2, as illustrated, ispreferable because the water pressure applied to the hollow fibermembrane 2 can be increased. Therefore, the solution gas 3 can besupplied at a relatively higher pressure while maintaining therelationship: the water pressure of the water to be treated 4>the gaspressure of the solution gas 3.

The gas dissolved water discharge piping 14 is connected to a gasdissolved water concentration meter 26 serving as a dissolved solutiongas concentration measuring means for measuring the concentration of thesolution gas 3 dissolved in the gas dissolved water 31, and the gasdissolved water concentration meter 26 sends a concentration signal 27to a second controller 28 serving as a second control means. The gasdissolved water concentration meter 26 measures the concentration of thegas dissolved water 31 after having been diluted. The second controller28 sends a second flow rate control signal 29 to the first flowregulator for the water to be treated 23 and the second flow regulatorfor the water to be treated 24. Upon receiving the second flow ratesignal 29, the first and the second flow regulators of the water to betreated 23 and 24 regulate the ratio of the flow rate Q1 of the water tobe treated 4 flowing through the first flow regulator for the water tobe treated 23 to the flow rate Q2 of the water to be treated 4 flowingthrough the second flow regulator for the water to be treated 24, sothat the concentration detected by the gas dissolved water concentrationmeter 26 can be controlled to the prescribed concentration.

The exhaust gas 6 exiting from the outer side of the hollow fibermembrane 2 is exhausted via exhaust gas piping 45. In the case that theexhaust gas contains a noxious gas, such an exhaust gas should betreated in a gas decomposing tower 30 filled with a catalyst or the like(not shown) to decompose the noxious gas before emitting the gas to theatmosphere.

An operation of the gas dissolved water producing apparatus 1 will nowbe described.

The solution gas 3 is supplied to the solution gas supply piping 12, andthe supplied solution gas 3 is, after the flow rate thereof having beenregulated by the solution gas flow regulator 16, delivered to the outerside of the hollow fiber membrane 2 incorporated in the processing tank11, at a prescribed flow rate. The water to be treated 4 is supplied tothe supply piping for the water to be treated 13, and the supplied waterto be treated 4 is compressed by the pump 17 and is passed through thefilter, where the foreign substances, if any, included in the water tobe treated 4 are eliminated, and further through the flow meter 19. Theflow rate Q of the water to be treated 4 supplied to the gas dissolvedwater producing apparatus 1 is measured by the flow meter 19, and theflow rate signal 20 is sent (fed back) to the first controller 21. Thefirst controller 21 determines a difference between a measured flow rateand a flow rate of a control target value, and sends a first flow ratecontrol signal based on the determined difference to the motor (notshown) for driving the pump 17, so that the motor may drive the pump 17at the controlled revolution speed.

The PID control system is employed to control the revolution speed ofthe motor in a stepless manner such that, for example, the revolutionspeed is increased if the measured flow rate is lower than the flow rateof the control target, and the revolution speed is decreased if themeasured flow rate is greater than the flow rate of the control target.

The water to be treated 4 passes through the flow meter 19, and then apart thereof (corresponding to the flow rate Q1) passes through theinner side of the hollow fiber membrane 2 in the processing tank 11 toflow into the first flow regulator for the water to be treated 23, andthe rest of the water to be treated 4 (corresponding to the flow rateQ2) flows into the bypass piping for the water to be treated 15 branchedoff from the supply piping for the water to be treated 13, and passesthrough the flow regulator for the water to be treated 24 to bypass thehollow fiber membrane 2. The water to be treated 4, which has absorbedthe dissolved solution gas 3 through the hollow fiber membrane 2 whilepassing through the inner side of the hollow fiber membrane 2 and thushas been formed into the gas dissolved water 5, is then discharged fromthe inner side of the hollow fiber membrane 2 and then flows through thegas dissolved water discharge piping 14 to join the water to be treated4 which has bypassed the hollow fiber membrane 2 at the joining section14A. Thus, the concentration of the dissolved solution gas in the gasdissolved water 5 is diluted. Further, the gas dissolved water 5 flowsthrough the gas dissolved water discharge piping 14 to be finallysupplied to cleaning equipment (not shown).

The gas dissolved water concentration meter 26 connected to the gasdissolved water discharge piping 14 measures the concentration of thedissolved solution gas after the dilution, and the gas dissolved waterconcentration meter 26 then sends a concentration signal 27 to thesecond controller 28. The second controller 28 determines the differencebetween a measured concentration and a concentration of a control targetvalue, calculates a second flow rate control signal 29 based on thedetermined difference by using an incorporated arithmetic circuit(though not shown) and sends the second flow rate control signal 29 tothe first and the second flow regulators of the water to be treated 23and 24 so as to accomplish control in the following manner.

That is, in effecting control, if the measured concentration is lowerthan that of the control target, the flow rate Q1 of the water to betreated 4 flowing through the inner side of the hollow fiber membrane 2(the flow rate passing through the first flow regulator for the water tobe treated 23) is increased, and the flow rate Q2 of the water to betreated 4 bypassing the hollow fiber membrane 2 (the flow rate passingthrough the second flow regulator for the water to be treated 24) isdecreased. If the measured concentration is greater than that of thecontrol target, then the flow rate Q1 of the water to be treated 4flowing through the inner side of the hollow fiber membrane 2 isdecreased and the flow rate Q2 of the water to be treated 4 bypassingthe hollow fiber membrane 2 is increased. The flow rates are controlledin this manner to adjust the concentration of the dissolved solution gas3 in the gas dissolved water 31 to the prescribed value. Controlling theconcentration of the dissolved solution gas 3 in the gas dissolved water31 to the prescribed value, results in controlling the pressure of thegas dissolved water 5, 31 to a prescribed pressure. It is to be notedthat, preferably, the overall gas dissolved water producing apparatus 1should be operated automatically.

If the concentration data of the water to be treated 4 and the saturatedgas dissolved water 5 are collected regularly and alternately at, forexample, the locations indicated as B and A in the drawing,respectively, and are continuously updated by using the gas dissolvedwater concentration meter 26 while the gas dissolved water 31 is notproduced, then the gas dissolved water 31 having the prescribed level ofdissolved solution gas concentration could be produced and supplied in ashort time, even in a case in which a dissolved solution gasconcentration of the water to be treated 4 supplied from the source ofthe water to be treated 8 is changed, or in a case in which the watertemperature and thus the dissolved solution gas concentration of thesaturated gas dissolved water 5 is changed.

For example, if a concentration of the solution gas desired to bedissolved, such as N₂ and O₂, in the water to be treated 4 from thesource of the water to be treated 8 is increased, a flow ratedistribution may be controlled such that the flow rate of Q1 isdecreased and the flow rate of Q2 for bypassing is increased. Similarly,if the concentration of the saturated gas dissolved water 5 isincreased, then the Q1 is decreased and the Q2 is increased. Further, ifthe water temperature of the gas dissolved water 5 is increased, thesaturated concentration of the gas allowed to remain as dissolved in thehollow fiber membrane 2 (see FIG. 2) will be substantially lowered, andthen the Q1 is increased and the Q2 for bypassing is decreased. A totalnumber of three dissolved solution gas concentration meters 26 formeasuring the concentrations of the water to be treated 4, the saturatedgas dissolved water 5, and the gas dissolved water after the dilution31, respectively, may be arranged on the basis of one for eachappropriate location. Alternatively, a single dissolved solution gasconcentration meter 26 may be employed, and the locations formeasurement may be switched between one another as needed. In thepreceding discussion, the dissolved gas concentration meter 26 may bearranged so as to measure the concentration and/or temperature of thegas dissolved water 31 alternatively.

In the gas dissolved water producing apparatus 1 according to thisembodiment, the ultrapure water to which the degassing process has beenapplied is preferably used as the water to be treated 4. In the presentapparatus 1, the concentration levels in the water to be treated 4 atthe inlet port of the supply piping for the water to be treated 13 arecontrolled to be below 3 ppm for nitrogen, below 100 ppb for oxygen, andbelow 1 ppb for hydrogen, respectively. The water to be treated 4 iscontrolled such that the supply flow rate Q is 20 to 30 L/min, thesupply temperature is in a range of 20 to 23° C., and the supplypressure is in a range of 0.20 to 0.30 MPa (2.0 to 3.0 kgf/cm²) (by gagepressure).

The nitrogen gas (case 1) or the hydrogen gas (case 2) each having anapproximately 100% purity were used as the solution gas 3. It ispreferable that the solution gas to be supplied has a purity of 99% orhigher. Alternatively, argon gas, oxygen gas or carbon dioxide gas maybe used as the solution gas 3. The supply pressure of the solution gas 3is 0.00 MPa (0.00 kgf/cm²) (by gage pressure), which is equivalent tothe ambient pressure. The supply pressure of the water to be treated 4is set to be higher than the solution gas pressure by 0.20 to 30 MPa(2.0 to 3.0 kgf/cm²). Setting the supply pressure of the water to betreated 4 to be higher than the solution gas pressure by 0.01 MPa (0.1kgf/cm²) or more can supply a gas dissolved water that includes nominute air bubbles or impurities and still has a uniform concentration.Preferably, the supply pressure of the solution gas 3 is typicallyhigher than the ambient pressure, because in this case the supply methodcan be simplified.

In the present gas dissolved water producing apparatus 1, a section incontact with the liquid is made of a non-metal material so as to avoid aproblem of metal ions being released into the water to be treated 4. Thepump 17 is controlled in a stepless variable speed controlling manner,and is designed as a non-particle type using a dynamic pressure bearingto eliminate any mechanical contacts of rotors so as to inhibitgeneration of minute particles from the inside of the pump. A highlypurified ceramic and a tetrafluoride resin are used for the material ofthe liquid contacting section to avoid a problem of metal ions beingreleased into the water to be treated 4. The filter 18 comprises amembrane filter having a nominal filtration rating of 0.05 μm. As forthe hollow fiber membrane, it is preferable to use a hollow fibermembrane made of Teflon, a porous hydrophobic membrane (pore sizedistribution of 0.01 to 1 μm) made of polytetrafluoroethylene or thelike. As for the material of the piping, it is preferable to use thepiping made of PVDF (polyvinylidenfluoride, fluororesin) which hasexcellent air-tightness and a relatively low permeability against thegas from the outside.

According to the gas dissolved water producing apparatus 1 of thepresent embodiment, if nitrogen gas is used as the solution gas 3 (case1), the gas dissolved water 31 having the nitrogen gas concentration of5 to 20 ppm (at the water temperature of 20° C.) can be producedefficiently in a short period. Alternatively, if hydrogen gas is used asthe solution gas (case 2), the gas dissolved water 31 having a hydrogengas concentration of 100 to 1000 ppb (at the water temperature of 20°C.) can be produced efficiently in a short period.

FIGS. 3 to 5 show experimental results from the measurement of theconcentrations varying over time in the case of using nitrogen gas (case1). Respectively, the figures illustrate the case for producing the gasdissolved water 31 having a concentration of 6ppm at a water temperatureof 20° C. (FIG. 3), the case for producing the gas dissolved water 31having a concentration of 10 ppm at the water temperature of 20° C.(FIG. 4), and the case for producing the gas dissolved water 31 having aconcentration of 13 ppm at a water temperature of 20° C. (FIG. 5). InFIGS. 3 to 5, the x-axis indicates the time (unit by minutes), and they-axis indicates the dissolved nitrogen gas concentration (unit by ppm).Further, in the respective drawings, the supply flow rate of the waterto be treated was set to be 20 L/min and the measurements were repeatedfour times, which are represented by the data {circle over (1)} to{circle over (4)}. In respective cases, as can be seen from the data,the gas dissolved water 31 of the targeted concentration can be producedin a time of around 1 to 1.5 minutes.

It is to be appreciated that if the solution gas is not a 100% purifiedgas, the concentration of the solution gas dissolved in the gasdissolved water would be a saturated concentration based on a partialpressure of the solution gas in the supplied gas. Needless to say, thegas supplied to the solution gas supply piping may be a mixed gas.

The first flow regulator for the water to be treated 23 in the supplypiping for the water to be treated 13 may be a control valve forcontrolling the flow rate in response to the second flow rate controlsignal 29 from the second controller 28. The second flow regulator forthe water to be treated 24 in the bypass piping for the water to betreated 15 may also be a control valve for controlling the flow rate inresponse to the second flow rate control signal 29 from the secondcontroller 28. Instead of the two control valves being disposedindependently in respective pipings, a single three-way control valvefunctioning as a flow rate controlling means of the water to be treatedmay be installed in the branch section 13A of the supply piping for thewater to be treated 13. In that case, the three-way control valve servesas the first flow rate regulating means as well as the second flow rateregulating means. In this regard, the branch section 13A is consideredto be a part of the supply piping for the water to be treated 13 and apart of the bypass piping for the water to be treated 15, as well.

It is to be appreciated that the gas dissolved water producing apparatus1 of the present invention may also be utilized as a degassed watersupplying apparatus by switching the flow directions such that all theflow toward the supply piping for the water to be treated 13 may bedirected and passed through the bypass piping for the water to betreated 15. Further, the apparatus according to the present inventioncan also produce a saturated gas dissolved water 31 by switching theflow directions so that all the flow originally directed to the supplypiping for the water to be treated 13 can be introduced into the innerside of the hollow fiber membrane 2. Although, in this embodiment, theapparatus has the configuration in which the supply piping for the waterto be treated 13 for producing the gas dissolved water 31 and the bypasspiping for the water to be treated 15 are branched off from the commonsource of the water to be treated 8, the present invention is notlimited to the particular mode shown in FIG. 1 in which the bypasspiping of the processing tank 11 is provided. In fact, one pipingsection of the water to be treated which is connected to the processingtank 11 for producing the saturated gas dissolved water and the otherpiping section of the water to be treated for dilution may be connectedto separate sources of water to be treated so as to be suppliedtherefrom, respectively.

Ultrasonic cleaning equipment for wafer 101, 102 will now be describedas an example for applying the gas dissolved water with itsconcentration controlled to be below the saturated concentration, whichhas been produced according to the present invention. The gas dissolvedwater obtained by way of the present invention is especially suitablefor cleaning device wafers.

FIG. 6 shows a perspective view of the ultrasonic cleaning equipment forwafer 101 serving as an ultrasonic cleaning device. Referring to FIG. 6,the ultrasonic cleaning equipment for wafer 101 comprises a rotary chuck140 having four chuck pawls 141 and a shaft 142 on which the rotarychuck 140 is mounted. The rotary chuck 140 is designed to carry asemiconductor wafer W1 thereon with the chuck pawls 141 clamping aperiphery WA of the wafer W1, and to rotate in the direction indicatedby the arrow X as centered on the shaft 142. The ultrasonic cleaningequipment for wafer 101 further comprises a cleaning liquid injectingnozzle 150, and is designed such that a cleaning liquid 151 may beinjected from the cleaning liquid injecting nozzle 150 against a surfaceto be cleaned WB of the semiconductor wafer W1 (hereinafter sometimesreferred to as an upper surface WB).

In the ultrasonic cleaning equipment for wafer 101, for example, afterhaving been polished, the semiconductor wafer WI is placed with thesurface to be cleaned WB up and securely clamped at the peripherythereof by the chuck pawls 141 of the rotary chuck 140. While the rotarychuck 140 is being rotated in the direction indicated by the arrow X,the cleaning liquid 151 is injected from the cleaning liquid injectingnozzle 150 against the upper surface WB of the semiconductor wafer W1 towash off abrasive grains and shavings held on the upper surface WB ofthe semiconductor wafer W1. Hereinafter, an application in the megasonic cleaning will be described.

FIG. 7 is a sectional view illustrating a detailed configuration of amega sonic cleaning nozzle 155 used in the ultrasonic cleaning equipmentfor a wafer 101 of FIG. 6. Referring to FIG. 7, the mega sonic cleaningnozzle 155 is configured such that an ultrasonic vibrator 157 is mountedon a rear end portion 156C of a nozzle main body 156 so as to functionas an ultrasonic wave transmitting device. When the ultrasonic vibrator157 is activated and the gas dissolved water 31 (see FIG. 1) from thegas dissolved water supply line 14 (see FIG. 1), after the concentrationthereof has been adjusted as shown in FIG. 1, is introduced into aninlet port 156A formed in the nozzle main body 156, thereby anultrasonic vibration energy is imparted to the gas dissolved water 31.Therefore, the cleaning liquid 151 (see FIG. 6) to which the ultrasonicvibration energy has been imparted can be injected from an injectionport 156B formed in the nozzle main body 156 against the upper surfaceWB of the semiconductor wafer W1. It is to be noted that the gasdissolved water 31 is injected as the cleaning liquid 151.

In this way, the ultrasonic energy is indirectly imparted to any dustexisting on the upper surface WB of the semiconductor wafer W1 throughthe injected cleaning liquid 151 (see FIG. 6). As a result, the dust onthe semiconductor wafer W1 is vibrated and released from the uppersurface WB of the semiconductor wafer W1, and will be washed away by theinjected cleaning liquid 151.

In this case, a gas dissolved water containing, for example, N₂ as thesolution gas may be used as the cleaning liquid. In that case, airbubbles are liable to be formed in the cleaning liquid if theconcentration of the gas dissolved therein is too high. In such an eventthat the generated air bubbles gather to form large air bubbles and/orthe generated air bubbles adhere to the surface being cleaned WB, theportion of the semiconductor wafer W1 having the air bubbles adheringthereto is prohibited from being cleaned uniformly as compared to theother portions of the wafer W1 having no air bubbles adhering thereto.

To deal with this case, if the gas dissolved water with itsconcentration controlled to be equal to or less than the saturatedconcentration is used in the above-discussed mega jet cleaning, as isthe case with the present invention, it may help inhibit the formationof air bubbles, or at least limit the formation of large-diameterbubbles. Thus, cleaning of the minute concavities and convexities on thedevice wafer having micro-fabricated patterns may be performed in agentle and uniform manner. In other cleaning cases, the gas dissolvedwater with the concentration not greater than the saturatedconcentration should preferably be used to clean a device waferparticularly having a micro-fabricated patterned surface.

FIG. 8 shows another example of ultrasonic cleaning equipment for wafer102 as an alternative embodiment of the ultrasonic cleaning device. Theultrasonic cleaning equipment for wafer 102 comprises a gas dissolvedwater producing apparatus 1, a cleaning bath 163, a cleaning liquidsupply line 160 interconnecting the gas dissolved water producingapparatus 1 and the cleaning bath 163, and a drain tank 170 arranged tohouse the cleaning bath 163 therein.

A gas dissolved water 31 (e.g., nitrogen containing water) with theconcentration thereof controlled to be no greater than the saturatedconcentration, which has been produced in the gas dissolved waterproducing apparatus 1 of the present invention, is supplied into thecleaning bath 163 from a cleaning liquid supply nozzle 162 attachedthereto via the gas dissolved water supply line 160.

The cleaning liquid supply nozzle 162 (see FIG. 9) is a cylindricalnozzle lying along an inner bottom surface 164 of the cleaning bath 163.This cleaning liquid supply nozzle 162 includes a plurality of dischargeports 165 along a longitudinal direction thereof (see FIG. 9), and thegas dissolved water 31 is supplied as the cleaning liquid 31 from thedischarge ports 165 into the cleaning bath 163. An ultrasonic vibrator166 functioning as an ultrasonic wave transmitting device is disposed ona lower face 169 of the cleaning bath 163, and the ultrasonic vibrator166 imparts ultrasonic vibration energy to the cleaning liquid 31 in thecleaning bath 163.

Typically, 25 device wafers W2 to be cleaned (for example, siliconwafers) are placed in the cleaning bath 163 in the vertically uprightposition. Then, the cleaning bath 163 is filled with the cleaning liquid31 and cleaning liquid which overflows from the cleaning bath 163 isrecovered in the drain tank 170 arranged to house the cleaning bath 163therein. The cleaning liquid 31 recovered in the drain tank 170 isdischarged from the drain line 167 connected to the drain tank. Theultrasonic cleaning equipment for wafer 102 of this embodiment providesan advantageous effect that a large number of device wafers W2 can becleaned quickly thereby improving a throughput, in addition to theadvantages similar to those provided by the preceding ultrasoniccleaning equipment for wafer 101.

ADVANTAGEOUS EFFECTS OF THE INVENTION

As discussed above, since the gas dissolved water producing apparatusaccording to the present invention comprises the solution gas supplychannel, the first supply channel for the water to be treated, thesecond supply channel for the water to be treated, and the gas dissolvedwater discharge channel, and because the second supply channel for thewater to be treated joins the gas dissolved water discharge channel sothat the water to be treated guided by the second supply channel for thewater to be treated can dilute the gas dissolved water until theconcentration of the solution gas in the gas dissolved water reaches aprescribed concentration, the gas dissolved water producing apparatus isable to rapidly and efficiently produce a gas dissolved water that has aconcentration of dissolved solution gas not greater than a saturatedconcentration.

As discussed above, the ultrasonic cleaning equipment according to thepresent invention comprises the gas dissolved water producing apparatusof the present invention and the ultrasonic wave transmitting device.Thus, when a workpiece to be cleaned is cleaned with the gas dissolvedwater produced by the gas dissolved water producing apparatus of thepresent invention, the ultrasonic energy is imparted to the gasdissolved water. Therefore, the gas dissolved water controlled to have asaturated concentration suitable for cleaning can be used as a cleaningliquid. Further, a gas dissolved water to which the ultrasonic energyhas been imparted can be used as a cleaning liquid, so that theworkpiece to be cleaned can be cleaned more cleanly.

1-13. (canceled)
 14. A polishing apparatus comprising: a rotatable chuckincluding chuck pawls to be clamped to a periphery of a semiconductorwafer so as to hold the semiconductor wafer; a cleaning liquid ejectingnozzle for ejecting a cleaning liquid against a surface of thesemiconductor wafer held by said rotatable chuck while said rotatablechuck rotates; and an ultrasonic cleaning device for cleaning thesemiconductor wafer using gas-dissolved water having a solution gasconcentration no greater than a saturated solution gas concentration.15. The polishing apparatus of claim 14, wherein said ultrasoniccleaning device includes a gas-dissolved water producing apparatusincluding: a dissolving section for dissolving a solution gas into waterto form gas-dissolved water; a solution gas supply channel for guidingthe solution gas into said dissolving section; a water supply channelfor guiding the water, said water supply channel including: a firstsupply channel for guiding the water into said dissolving section; and asecond supply channel for guiding the water around said dissolvingsection so that the water does not pass through said dissolving section,said second supply channel being branched off from said first supplychannel so as to form a bypass around said dissolving section; agas-dissolved water discharge channel for guiding the gas-dissolvedwater from said dissolving section, said second supply channelcommunicating with said gas-dissolved waterdischarge channel so that thewater bypassed around said dissolving section flows into thegas-dissolved water to thereby dilute the gas-dissolved water; a flowrate regulator arranged in said gas-dissolved water discharge channeldownstream of said dissolving section, for regulating a flow of thewater guided through said water supply channel; and a dissolved solutiongas concentration meter for measuring the solution gas concentration ofthe gas-dissolved water in said gas-dissolved water discharge channel.16-18. (canceled)
 19. A polishing method comprising: polishing asemiconductor wafer; after said polishing, securely clamping a peripheryof the semiconductor wafer using chuck pawls of a rotatable chuck sothat the semiconductor wafer is held by the rotatable chuck with asurface to be cleaned facing upwards; rotating the rotatable chuck;ejecting cleaning liquid from a cleaning liquid ejecting nozzle againstthe surface of the semiconductor wafer facing upwards so as to wash offdebris from the surface of the semiconductor wafer; and cleaning thesemiconductor wafer with an ultrasonic cleaning device usinggas-dissolved water having a solution gas concentration no greater thana saturated solution gas concentration.
 20. The polishing method ofclaim 19, wherein said cleaning of the semiconductor wafer with anultrasonic cleaning device using gas-dissolved water comprises producinggas-dissolved water using a gas-dissolved water producing apparatus,including: a dissolving section for dissolving a solution gas into waterto form gas-dissolved water; a solution gas supply channel for guidingthe solution gas into said dissolving section; a water supply channelfor guiding the water, said water supply channel including: a firstsupply channel for guiding the water into said dissolving section; and asecond supply channel for guiding the water around said dissolvingsection so that the water does not pass through said dissolving section;a gas-dissolved water discharge channel for guiding the gas-dissolvedwater from said dissolving section, said second supply channelcommunicating with said gas-dissolved water discharge channel so thatthe water that does not pass through said dissolving section flows intothe gas-dissolved water to thereby dilute the gas-dissolved water; aflow rate regulator arranged in said water supply channel, forregulating a flow of the water guided through said water supply channel;a dissolved solution gas concentration meter for measuring a solutiongas concentration of the gas-dissolved water in said gas-dissolved waterdischarge channel; and a controller for controlling said flow rateregulator based on the solution gas concentration measured by saiddissolved solution gas concentration meter. 21-25. (canceled)